Such a roller blind comprises an apron formed of hinged blades the side ends of which slide internally along side grooves when the apron passes from an unfolded position into a position of winding-up around a shaft, and vice-versa, under the action of motorization means.
Within the framework of this invention, said motorization is autonomously supplied with current through batteries. In addition, the latter can be designed rechargeable in the form of accumulators. Their recharging can namely occur through a sensor for converting renewable energy, such as a photovoltaic sensor converting solar energy, a wind dynamo or the like.
The major difficulties of an autonomously supplied device reside in optimizing its operation time while preserving a high reliability. Within the framework of a roller blind according to the invention, the autonomy should be as large as possible, so that the user can actuate said blind when he wishes so, irrespective of the weather conditions. Nevertheless, improving the autonomy, for example through energy saving, should not occur to the detriment of the operation of said blind. Its use indeed requires a reasonable time of displacement of the blind and, hence, a suitable unfolding and winding-up speed.
Within this specific framework of the invention, it has been devised to recover the potential energy of gravity from the blind during its sliding from the wound-up position into the unfolded position. The conversion of this energy permits to recharge the batteries and considerably improves the autonomy of the roller blind.
During this unfolding of the roller-blind apron, several phases are present, a first phase requiring driving the roller blind in order to push back the slats of the apron into the lateral guiding grooves. This first phase is followed by a second phase in which the weight of the apron already inserted into the side grooves becomes large enough to ensure the driving and, hence, the unfolding of the roller blind; during this second phase, the motor acts more as braking means, so as to limit the downward-travel speed of the apron and to avoid the risks of accident as well as the impact when the apron comes to a stop at the lower end of these side grooves. At that time follows a third phase in which the pulling force exerted by the apron onto the winding-up shaft progressively tends to diminish, corresponding to the piling up of the slats of said apron above each other.
It should be noted in this respect that said slats are often movable with respect to each other in a direction perpendicular to their longitudinal axis, in order to impart to the roller blind, as the case may be, an openwork or a fully closed position. Indeed, in a position spread apart from each other, these slats leave openings favouring the passing through of light and ensure some ventilation.
During this third phase the motor can progressively pass from a braking function to once again a driving function, depending on the hanging weight of the apron and the frictions the latter is subjected to.
The energy recovery can occur when the motor ensures a braking function. However, one easily understands that the pulling force exerted by the apron constantly changes. This also applies to the braking power. Therefore, the recoverable power is in turn highly varying.